What Creates a Deadly Mudslide?

A mudslide along the Stilliguamish River in Washington State measured at least 135 feet wide and 180 feet deep and plowed through homes.

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Although deadly, Hurricane Isaac scourged Louisiana with less ferocity than Hurricane Katrina did seven years ago. Katrina was one of American history's deadliest and costliest natural disasters. Part of what made Katrina such a tragedy was the inadequate emergency response from authorities. However, as intense as the outcry over the response to Katrina was, it pales in comparison to the repercussions of when one of history's deadliest storms struck what is now Bangladesh.
Bangladesh was a part of Pakistan at that time, but the people of East Pakistan, as the region was called, suffered discrimination from the western portion of the nation and revolution was smoldering. The flames of nationalism and rebellion were fanned by the high winds of the massive Bhola cyclone which rushed in from the Bay of Bengal on November 10, 1970.
The Pakistani government was criticized by locals and in the international media for failure to provide adequate disaster relief to East Pakistan, which may have contributed to the 300,000 to 500,000 people who perished in the storm and its aftermath. Soon after the cyclone, the storm of East Pakistan's outrage built into a war that tore Pakistan apart. The torment of war raged on until Bangladesh emerged as an independent nation from the flood of bloodshed that was the Bangladesh Liberation War.
Throughout history massive storms have toppled human ambitions and left suffering and death in their wake. Particular natural disasters stand out from the line up of perpetrators as particularly devastating natural born killers.

Hurricane Isaac approached the Louisiana and

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The Day America Burned
The wildfires that incinerated stretches of the American west this year were huge, but relatively few people lost their lives. On October 8, 1871 more people died in the flames of a wildfire than on any other day in recorded human history. On that day the Peshtigo Fire started in the forests of Wisconsin and was spread by a strong wind. The blaze quickly grew as it fed on trees left parched by a summer drought. The flames weren't extinguished until after they had snuffed out the lives of 1,200 – 2,500 people. The exact number is unknown because local records were also destroyed. The entire town of Peshtigo was consumed, leaving few to identify the charred corpses.
On the same day, the Great Chicago Fire reduced much of the Windy City to ashes. Though Mrs. O'Leary's cow was later cleared of any culpability, the story of a kicking cow starting the fire became part of the legend surrounding the blaze that killed 300.
PHOTOS: Western Wildfires

Smoke rises from the Flagstaff Fire on the ou

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Nature's Gas Chamber
Other natural disasters can destroy whole towns at once too. Besides malaria, venomous snakes and leopards, the forest of Cameroon is also home to a lake that kills villages with its belches.
Lake Nyos released an estimated 1.2 cubic kilometers (0.29 cu. mi.) of carbon dioxide and noxious sulfurous gases on August 21, 1986. As the bubble of heavier-than-air gas spread along the ground, approximately 1,700 people were suffocated along with 3,500 livestock. The killing cloud spread death up to 25 km (16 mi) from the lake.
The lake's gas problem comes from an underwater magma dome that is constantly leaking carbon dioxide into the water. As the concentration builds, a disturbance in the lake's waters can cause the gas to be released in a suffocating explosion. Now, a degassing system siphon's the gas saturated deeper waters up to the surface, where the gas escapes in harmless quantities.
PHOTOS: Eruption of Iceland's Grimsvotn Volcano

Lake Nyos, less than two weeks after the dead

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4000 With One Bolt
The Knights Hospitaller became the Knights of Rhodes after they lost control of Jerusalem to Muslim armies during the Crusades. They set up shop on the island of Rhodes in the 14th century by constructing a massive castle known as the Palace of the Grand Master of the Knights of Rhodes. The Knights also lost that stronghold to Muslim armies after the Turks conquered the islands and expelled not only the knights, but also the Greeks.
Being expelled may have saved their lives. On April 3, 1856, a single bolt of lightning struck the steeple of the church attached to the palace. The Turks had been using the church and the storage area beneath the Palace as an ammo storehouse. When the fire found the gunpowder, an explosion leveled the 450 year old Palace and laid low 4,000 people.
The Palace was rebuilt by the Italians in the early 20th century after they gained control of the island in 1912. The refurbished castle had the dubious distinction of hosting vacationing dictator Benito Mussolini after the Fascists rose in Italy.
PHOTOS: New World Heritage Sites

The rebuilt Palace of the Grand Master of the

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China Shattered by Quake
Historical records in China extend unbroken for centuries. Included in those records are the body counts from some of the worst disasters in human history.
An earthquake centered in Shaanxi province killed approximately 830,000 people on the morning of Jan. 23, 1556. In some areas, more than half the population was wiped out. One reason the toll was so high was that many residents lived in artificial caves dug into the soft soils of the area. The powdery soil collapsed in the quake, turning family homes into mass graves.
Beneath those Shaanxi soils, the terracotta army of Qin Shi Huang, China's first emperor, may have been shaken from their slumber by the heaving of the earth around them and the misery of their country above them.
ANALYSIS: The Pain and Beauty of China's "Earthquake Marriages"

Pit 1 of the excavation of the terracotta arm

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China Drowned by Flood
Floods have also terrorized the Chinese many times in the country's long history. Six of the ten deadliest floods in history struck the Middle Kingdom between 1887 and 1975. The worst may have been the flood of 1931. Estimates range as high as four million dead.
The 1931 flood occurred after a two year drought ended. Heavy snows in the winter led into a rainy spring and even wetter summer during which seven typhoons drenched the land. The Yellow (Huang He), Yangtze (Chang Jiang) and Huai Rivers all flooded and inundated much of the country's cropland. Whole villages were washed away as dikes and levees failed.
PHOTOS: Freak Beijing Storm Brings Severe Floods

Monument to the people of Wuhan, China overco

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A Wave of Death
Earthquakes and inundations can be deadly on their own, but together they pack a one-two punch of devastation.
On Dec. 26, 2004, the third largest earthquake ever measured unleashed a wave that would wash away more lives than any other in history. More than 230,000 people died as the tsunami spread across the Indian Ocean from the quake's epicenter off the western coast of Sumatra, Indonesia. Fourteen countries were affected by the wave, especially Indonesia, Sri Lanka, India and Thailand.
PHOTOS: Japan Earthquake and Tsunami: Before and After

Trash and debris cover the streets near homes

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Ring of Fire
For those countries that fall into the true ring of fire, the only man in black is the Grim Reaper, not Johnny Cash. The ring of fire is a line of volcanoes around the perimeter of the Pacific Ocean where tectonic forces make earthquakes and volcanoes an ever present threat.
Indonesia shines like a jewel of molten magma set in the ring of fire. During the past 500 years, the area that is now Indonesia has suffered more deadly volcanic eruptions than any other place. An ancient eruption of an Indonesian volcano in the 400s AD may have darkened the skies over an already crumbling Roman Empire and led to crop failures.
More recently, nearly 100,000 perished in the eruption of Mount Tambora in 1815. The eruption darkened the global sky and caused the Year Without a Summer, when chilly temperatures again led to failed crops in Europe.
The island of Krakatoa exploded in a gigantic eruption in 1883 that ended 36,000 lives. Mount Kelut killed more than 5,000 in 1919. The same volcano had taken out 10,000 people in 1586.
PHOTOS: Earth Perspectives Through the Ages

Was it a landslide, landslip, mudslide or mud flow, and was there any way to prevent the catastrophe that killed at least 14 people on Saturday along the Stilliguamish River in Washington State?

"This will be the worst landslide in the U.S.A. for many years," predicted David Petley, a landslide researcher at Durham University in the U.K. and author of The Landslide Blog. By worst he means in terms of deaths, not the size of the landslide. "The last event on a similar scale of which I am aware was the 25th December, 2003, debris flow in San Bernadino County, California, which killed 16 people. It looks likely that this landslide will be worse."

Petley also calls the disaster a "landslip." So which is it? Both, actually.

We've been to the moon but we've barely scratched the surface of our own planet!

DCI

Landslide and landslip are both terms used to cover a lot of different kinds of movements in the land, with landslide being the most popular word. But the movements encompass everything from a slump (a slow sagging of a hillside that can be measured on a calendar) to a rock fall (where chunks of rock can reach terminal velocity).

The term mudslide works too, except that the mud describes the bottom, deadly part more than the upper part of the event.

In the Stilliguamish case, the hillside is made of loose sandy material laid down by glacial lakes less than 16,000 years ago, according to Washington State geologist Dan McShane of Stratum Group who writes a blog called Reading the Washington Landscape. Since then the Stilliguamish River has cut down into that loose material, creating hillsides of the sandy material that have a history of collapsing.

Those hillsides were apparently saturated with water when the one collapsed on Saturday. As anyone knows who has tried to build a sand castle, too much water causes the sand to flow and not stand up. In microscopic terms, it's the grain-to-grain friction that holds sandy slopes together. When water fills the spaces between the grains and pushes the grains apart, the sand, and in this case an entire hillside, collapses.

The upper part of the Stilliguamish/Oso landslide appears to have slumped, and rotated -- like a person sliding down off a chair. The lower portions were even wetter and apparently behaved more like liquid -- a mudflow.

In fact, there's evidence that the landslide released a great deal of water at its base as it occurred. The National Weather Service tweeted an image of data from a nearby river gauge on the Stilliguamish River showing a spike in the water level at the time of the landslide, followed by a dramatic drop in the river. The latter was caused by the landslide damming the river.

"This landslide area is well known and has been a big problem for the past roughly 20 years," explained McShane. "I looked at this slide area last summer. It was clearly bad news then and with very heavy multiple rain events the past six weeks landslides -- particularly big ones -- are not a surprise."

That history prompted Petley to wonder, in an email to Discovery News, whether the deaths from this landslide could have been avoided.

"Whilst I am referring to this as the Oso landslip, in fact it is a reactivation of an existing landslide, known as the Hazel Landslide," Petley reported in his blog. "This landslide is known to have moved in 1988, and went through a second phase of movement in 2006. It is well described in a blog post from 2009."

All of which suggests that there is a dangerous gap between the science and the way the land is being used in the Stilliguamish Valley, and perhaps elsewhere.